Many hearing impaired people have difficulties understanding different voices. Most amplification techniques (including generic fitting rationales) are developed around an average long term spectrum of speech (e.g. NAL NL1 (National Acoustic Laboratories, AU), DSL m[i/o] (Desired Sensation Level, The University of Western Ontario CDN), etc.) of a male voice without regards to any characteristics of the individual speaker's voice. Recorded speech tests used for the verification of the hearing aid fitting typically do not take into account any individual variations, i.e. an average is used. Anecdotally, in the clinic, the male voice is often reported by end users of hearing aids to be easier to understand than a female or a child's voice.
US 2004/0190740 describes a time and frequency dependent method of adjusting the amplification of a hearing aid to a particular speech signal in a noisy environment. The method is based on determining the levels of speech and noise signals in a plurality of frequency bands and subsequent ‘automatic’ adjustment of the electrical signal dependent thereon.
U.S. Pat. No. 6,453,284 describes a system for tracking individual voices in a group of voices by estimating the fundamental frequencies of each of the voices present. The system involves the use of a recurrent neural network to track the multiple voices over time. The system can e.g. be implemented in a digital hearing aid for selective amplification of an individual's voice.
EP 1 530 403 describes the definition of various groups of acoustical signals and the automatic determination of the type of acoustic signal present in a given situation and the adaptation of a corresponding fitting signal to the HA.